FIG. 9 shows a first example of a conventional cooling apparatus used for a heat exchanger, that is, a cooling apparatus for a radiator. This cooling apparatus has been illustrated in JP-A-58-18023 (UM). In FIG. 9, a radiator 81 normally mounted on a Diesel engine (not shown) is utilized for exchanging heat between the Diesel engine and cooling water flowing in the internal part of the radiator 81 in order to cool the Diesel engine. The radiator 81 has a fan 83 for producing an airflow 82 and a shroud 84 for leading the airflow 82 to the body of the radiator 81. The fan 83 is a type of axial fan. The shroud 84 has a cylindrical opening portion 84a for introducing air from the outside, a cylindrical/four-cornered housing 84b connected to the cylindrical opening portion 84a, and a four-cornered ring edge portion 84c connected to both the housing 84b and the body of the radiator 81. The housing 84b is formed so that an area of an opening thereof in transverse cross section to its axis expands exponentially from the opening portion 84a to the edge portion 84c. Accordingly, the shape of the cylindrical/four-cornered housing 84b is nearly the horn-shape of a quadrangular pyramid. The fan 83 is disposed in the internal space of the cylindrical opening portion 84a of the shroud 84. The fan 83 is rotated by a rotation-drive unit (not shown) so as to produce the airflow 82 based on drawing air from the outside. The airflow 82 can be gradually expanded in accordance with the shape of the housing 84b, which causes turbulence generated in the airflow 82 to decrease. The shape of the housing 84b makes the rate of the airflow 82 at every point inside thereof nearly uniform.
In the above-mentioned cooling apparatus for the radiator, the shape of the opening portion 84a close to the end of the fan-blades is formed to be cylindrical. Consequently, the conventional cooling apparatus for the radiator has a large air-passing resistance at the opening portion 84a. When rotating the fan 83 at the conventional rotating speed, the large air-passing resistance reduces the amount of the airflow and therefore brings a problem such that the conventional cooling apparatus cannot cool the Diesel engine effectively.
FIG. 10 shows a second example of a conventional cooling apparatus for the radiator. This type of cooling apparatus has been illustrated in JP-A-4-269326. In this cooling apparatus, a fan 92 is disposed near to a radiator 91 and rotated by an engine 93. A shroud 94 is arranged for enclosing and accommodating the fan 92 in the space between the radiator 91 and the engine 93. The fan 92 is a type of inclined axial fan provided with a taper hub. A part 94a of the shroud 94, which is near to the respective pointed ends of a plurality of blades 92a and surrounds the fan 92, has a bell-mouth form. This part 94a is hereinafter referred to as "a fan surrounding part 94a". The bell-mouth form of the fan surrounding part 94a is such that a radius thereof is gradually decreased as advancing from the left and right end portions to the middle portion, and hence there is a smallest radius at a specified point. That is, the fan surrounding part 94a is like a cylindrical body whose middle portion is drawn in toward its inside direction.
Here, when the width of the blade 92a of the fan 92 is L.sub.1 and the distance between the smallest radius portion and the radiator-side portion of the fan surrounding part 94a is L.sub.2, as shown in FIG. 10, a ratio given by L.sub.2 /L.sub.1 is defined as "a covering rate" which is expressed by a ratio or a percentage. The covering rate in the conventional cooling apparatus used for the radiator illustrated in JP-A-4-269326 was set to be 40% as an optimum value (with the permissible range from +10% to -20%).
In the second example of the conventional cooling apparatus for a radiator, the inclined axial fan has been used to generate a large flow of cooling air with a high pressure, and further the covering rate thereof has been set to be the most suitable value in order to achieve the highest cooling ability of the inclined axial fan. In accordance with the configurations of the second example, the problems in the first example of the conventional cooling apparatus can be solved.
However, in the second example of the conventional cooling apparatus, since an inclined axial fan is used as the fan 92, there is a problem that the brake horsepower of the fan 92 increases and the fuel expenses of the engine 93 rise.
Furthermore, in the second example of the conventional cooling apparatus, it is required to reduce a clearance (hereinafter referred to as "clearance") between the fan 92 and the fan surrounding part 94a of the shroud 94 in order to get sufficient cooling ability from the fan 92. When the clearance is relatively small, it is desirable that the shroud 94 is installed on the engine 93 equipped with the fan 92 rather than on the radiator 91 in order to maintain the clearance appropriately. The configuration concerning the clearance is clearly determined by the positional relationship between the fan 92 and the fan surrounding part 94a, and therefore the clearance can be suitably realized by installing the shroud 94 and the fan 92 on the common member. In other words, when fixing the shroud 94 to the radiator 91, it will be difficult to realize the suitable clearance because there is a possibility of producing an error due to practical installation of the radiator 91 and the engine 93. Then, in the second example, the shroud 94 is installed on the engine 93 by the part 94b of the shroud 94 extending to the engine 93. This configuration of the second example, however, poses a problem that the working efficiency in assembling the cooling apparatus is decreased and the production cost thereof is increased.
A main object of the present invention is to provide a cooling apparatus for a heat exchanger in which the brake horsepower of the fan can be suitably decreased and the fuel expenses of the engine can be sufficiently reduced.
Another object of the present invention is to provide a cooling apparatus for a heat exchanger in which assembly work efficiency can be increased and production cost can be decreased.
Another object of the present invention is to provide a cooling apparatus for a heat exchanger in which a shape of a fan surrounding part in a shroud is most suitable and a maximum of cooling ability can be attained.
Another object of the present invention is to provide a heat exchanger having a shroud which serves as a part of a cooling apparatus, in which the configuration of the shroud can reduce fuel expenses of an engine and the production cost and improve working efficiency of assembling the cooling apparatus.